Abstract
The Atlantic Forest is an excellent case study for the elevational diversity of birds, and some inventories along elevational gradients have been carried out in Brazil. Since none of these studies explain the patterns of species richness with elevation, we herein review all Brazilian studies on bird elevational diversity, and test a geometric constraint null model that predicts a unimodal species-altitude curve, the Mid-domain Effect (MDE). We searched for bird inventories in the literature and also analysed our own survey data using limited-radius point counts along an 800 m elevational gradient in the state of São Paulo, Brazil. We found 10 investigations of elevational diversity of Atlantic Forest birds and identified five different elevational patterns: monotonic decreasing diversity, constant at low elevations, constant at low elevations but increasing towards the middle, and two undescribed patterns for Atlantic Forest birds, trough-shaped and increasing diversity. The average MDE fit was low (r² = 0.31) and none of the MDE predictions were robust across all gradients. Those studies with good MDE model fits had obvious sampling bias. Although it has been proposed that the MDE may be positively associated with the elevational diversity of birds, it does not fit the Brazilian Atlantic Forest bird elevational diversity.
Highlights
The complex elevational diversity of birds has been investigated on every continent (GRINNELL & STORER 1924, ORIANS 1969, KIKKAWA & WILLIAMS 1971, TERBORGH 1971, LACK 1976, WARTMANN & FURRER 1977, PRIGOGINE 1980, THIOLLAY 1980, EGUCHI et al 1989, GOODMAN & GONZALES 1990, THORMSTROM & WATSON 1997, NATHAN & WERNER 1999, ALIABADIAN et al 2008)
The Mid-domain Effect (MDE) predicts 1) a unimodal diversity curve with maximum diversity at mid-elevations, 2) a strong positive association between the predicted diversity based on Monte Carlo simulations and the empirical diversity at each 100 m elevational band, 3) that deviations in maximum species richness away from the mid-point of the mountain should be distributed on random elevations of this mountain if spatial constraints alone drive elevational diversity and 4) a strong relationship between MDE fit (r2 value) and the ratio of the average bird range size to elevational gradient length
While many studies have supported the predictions of the MDE for many taxa (LIEBERMAN et al 1996, RAHBEK 1997, KESSLER 2000, 2001, HEANEY 2001, JETZ & RAHBEK 2001, SANDERS 2002, MCCAIN 2004, GARCÍA-LOPEZ et al 2011), others have rejected it, partially or entirely (BOKMA & MÖNKKÖNEN 2000, BROWN 2001, KOLEFF & GASTON 2001, BOKMA et al 2001, DINIZ-FILHO et al 2002, HAWKINS & DINIZ-FILHO 2002, LAURIE & SILANDER 2002, ZAPATA et al 2003, HERZOG et al 2005, ALIABADIAN et al 2008, MCCAIN 2009, 2010), arguing that it assumes an a-priori distribution of species (HAWKINS & DINIZ-FILHO 2002, ZAPATA et al 2003), and that some assumptions of the MDE are unrealistic, conceptually flawed, or internally inconsistent
Summary
The complex elevational diversity of birds has been investigated on every continent (GRINNELL & STORER 1924, ORIANS 1969, KIKKAWA & WILLIAMS 1971, TERBORGH 1971, LACK 1976, WARTMANN & FURRER 1977, PRIGOGINE 1980, THIOLLAY 1980, EGUCHI et al 1989, GOODMAN & GONZALES 1990, THORMSTROM & WATSON 1997, NATHAN & WERNER 1999, ALIABADIAN et al 2008). Apart from HOLT’s (1928) ornithological survey of the Serra do Itatiaia, in Rio de Janeiro, and STOTZ’s et al (1996) review of the elevational diversity of all birds in the Atlantic Forest, others have investigated bird elevational diversity in both mountain ranges of the Atlantic Forest (GOERCK 1999, BUZZETTI 2000, DEVELEY 2004, RAJÃO & CERQUEIRA 2006, MALLET-RODRIGUES et al 2010), and at other locations within these forests (BENCKE & KINDEL 1999, MELO-JÚNIOR et al 2001).
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